Pluto's realm (5)
I believe the answer is:
hades
'pluto's realm' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for hades that I've seen before include "It's hell in the Greek shade" , "gloomy place" , "In Greek myth, the Underworld" , "It's classical hell in the shade" , "Greek underworld with spirits of the dead" .)